Production of menthene



Patented Aug. 8, 1933 UNITED STATES PRODUCTION OF MENTHENE WalterSchoeller and Erwin Schwenk, Berlin- Westeiid, and Erich Borgwardt,Berlin-Pankow,

Germany, A. (3%., Berlin, Germany assignors to Schering-Kahlbaum NoDrawing. Application March 13, 1931, Serial No. 522,518, and in GermanyMarch 20, 1930 3 Claims.

Our invention refers to the production of a menthene compound and moreparticularly to the production of B-menthene. It is an object of ourinvention to produce 3-menthene from more readily available substancesin a particularly simpl and ellicient manner.

Broadly spoken our invention consists in bringing about anintramolecular rearrangement of l-menthene by subjecting it at elevatedtemperature and preferably at a temperature above 300 to the influenceof a suitable catalyst. Under such conditions a mixture of variousisomers of menthene, -90% of which are S-menthene, may be obtained andseparated from such mixture, for instance by fractionation. The firstand the last fractions which chiefly consist of 1- and 2-menthene may bereused in cycle for the production of further quantities of B-menthene.

The reaction underlying the present invention apparently proceeds asfollows:

In carrying out our invention we prefer to lead the vapor of l-mentheneor of a mixture of l-menthene and other isomers of menthene at anelevated temperature over a suitable contact mass. Temperatures of300-359 C. have been ascertained to furnish good results, but thetemperature may be raised up to 450 and above, or lowered down to 250and below Without sacrificing the advantages of our invention.

The catalyst may consist of suitable bodies of great surface area perunit of volume, such as pumice stone, bricks, silica gel (1. e.activated silicic acid), of bleaching clay, fullers earth, of zeolites,such as for instance the sodium aluminium silicate marketed under thetrademame tonsil, or the like. These bodies which are known under thename of surface catalysts may be mixed or impregnated with or replacedby suitable metal compounds, such as the oxides, sulfates or phosphatesof metals such as magnesium, copper and the like.

The time of contact between the menthene vapor and the catalyst shouldbe regulated in accordance with the temperature and activity of thecatalyst, and the vapors are then treated for the separation therefromof the B-menthene. To this end We may first cool them for the recoveryof a liquid mixture containing several or all of the menthene isomers,and thereafter fractionally distill the liquid for the separation ofsubstantially pure 3-menthene. The other fractions, which consist partlyof unaltered 3-menthene and partly of other isomers such the Z-menthene,may be once more sub 6 jected to the treatment according to the presentinvention, so that substantially all the l-menthene originally used isrecovered in the form of S-menthene.

We prefer adding these fractions to further quantities of l-menthene tobe treated, the process being thus carried out in cycle.

Example 1 100 grs l-menthene are led at a temperature of 450 C. over acatalyst consisting of pumice fragments and the vapors arising in thistreatment are treated once more in the same Way. After some hours thereaction mixture obtained is fractionated and about 87% of 3-menthene isobtained in the form of a colorless liquid boiling at 167-169".

Example 2 200 grs l-menthene are led at a temperature of about 320-350C. over a catalyst consisting of granulated copper phosphate which hasbeen mixed with about by weight phosphoric acid. The liquid reactionproduct is fractionally distilled and 56-60% of substantially pureS-menthene'boiling at 166-168" C. are-collected. The first and the lastfractions are mixed and led once more over the catalyst.

Example 4 300 grs L-menthene are led at a temperature of 300-350 C. overa catalyst obtained by superficially oxidizing copper shavings, i. 6.over a catalyst substantially consisting of copper oxide. A liquidreaction product is obtained from which 3-menthene may be separated asdescribed with reference to Example 1.

Example 5 prising acting on l-menthene at a temperature between 250 and450 C. with a surface catalyst and separating 3-menthene from themixture resulting in the reaction.

2. The method of producing 3-menthene comprising leading l-menthene at atemperature between 250 and 450 C. over a surface catalyst andseparating 3-menthene from the mixture resulting in the reaction.

3. The method of producing 3-menthene comprising leading l-menthene at atemperature between 300" and 450 C. over a surface catalyst andseparating 3-menthene from the mixture resulting in the reaction.

WALTER SCHOELLER. ERWIN SCHWENK. ERICH BORGWARDT.

